Let them talk, take the advise you do like and dismiss the parts of it that you don't want to do. Do what you want. I don't have anyone wanting me to turn quilting into a business...but I know the feeling of having an older sister that feels the need to constantly "give advise". She not only does it to me, but her children and it drives us all crazy. She always has a better way than your way.
I have learned...don't argue, don't agree, don't try to explain or justify why I do some things a certain way. I usually just say hmmmm or "really", she walks off happy thinking she has really helped me and I ignore the parts of her advise that I have no intention of doing. Since I have used this process, I am happier. She usually forgets about the discussion and it does not cause the conflicts when we argue our opinions.
When you turn a hobby into a business, it can take the fun away especially when you are not making enough money for your time. We all need something to get our minds free and even when I am frustrated over mistakes (I am a champion ripper), quilting is my release from life's little challenges.
I have had people want to pay me to make a quilt. When I start telling the going price for fabric and longarm prices not counting my time, that usually short circuits the conversation. Quilting is relaxing to me and that is why I don't sell my quilts. I do give away children and baby quilts and some lap quilts and a couple of bed quilts. I don't want the pressure of deadlines, misunderstandings, collecting payment and dealing with crazy people. I also do not want to spend time building a business when I could be quilting. Unless you design or write books, I would think it would be hard to make money making quilts. I would give you a quilt before I would sell one and get less than the value of materials and my time.
Your Dad and Sister both probably mean well and truly think they are "helping" you. Only you can make the decisions that are right for you. Got a baby quilt to rip apart..sewed a row upside down and did not notice until I was putting last border on. ^%$@#%&* Hope this book helps you. The End.